The advent of molecular imaging approaches such as Positron Emission Tomography (PET) has enabled measurements of molecular and cellular mechanisms throughout the body in preclinical and clinical settings. Such measurements have widespread diagnostic utility and their use for evaluation of treatment responses and to assist drug development is expanding rapidly. Recent studies in mice have documented the feasibility of using PET to visualize immune responses. We and others have demonstrated that anti-tumor T cell immunity can be monitored using PET reporter gene imaging. Similar approaches may enable evaluation of T cell trafficking thus expanding to use in patients undergoing cancer immunotherapy. Nonetheless, development of novel probes that allow for direct measurements of immune function would significantly widen the utility of PET imaging. Various cell surface receptors and intracellular enzymes may potentially be imaged by PET using specialized probes. Recently, in a mouse model of autoimmune demyelination, we showed that a probe for glycolysis called [18F]fluorodeoxyglucose ([18F]FDG) enables PET-based monitoring of disease onset via distribution of the probe in organs and of immunosuppressive therapy. However, [18F]FDG accumulates in non-lymphoid tissues including the heart, brain, and liver. This invention concerns the development of assays and novel probes to monitor biochemical cascades involved in fundamental cellular events such as proliferation, apoptosis, malignant transformation or lymphocyte activation.